Device for purifying the exhaust gas of an internal combustion engine

ABSTRACT

In a device for purifying the exhaust gas of an internal combustion engine, a first auxiliary catalytic apparatus is arranged in one of the two exhaust passages upstream of the exhaust gas merging portion, a second auxiliary catalytic apparatus is arranged in the other of the two exhaust passages, an amount of catalyst carried on the second auxiliary catalytic apparatus is smaller than that on the first auxiliary catalytic apparatus, and only the cylinder-group corresponding to the one of the two exhaust passages is operated at the engine start.

FIELD OF THE INVENTION

The present invention relates to a device for purifying the exhaust gas of an internal combustion engine.

DESCRIPTION OF THE RELATED ART

When all cylinders of a multi-cylinders engine, for example, such a V type engine are divided into two cylinder-groups and each of the two cylinder-groups is provided with an exhaust manifold, each cylinder-group is provided with an exhaust passage from each exhaust manifold to an exhaust gas merging portion. A main catalytic apparatus is arranged downstream of the exhaust gas merging portion to purify a large amount of exhaust gas in high engine load operation. However, the main catalytic apparatus is positioned far from the engine body and thus the temperature of the exhaust gas flowing into it is lowered. Therefore, when the temperature of exhaust gas is naturally low, in low engine load operation and the like, exhaust gas at a considerably low temperature flows into the main catalytic apparatus to deteriorate the activation degree of the catalyst and thus the main catalytic apparatus cannot purify the exhaust gas sufficiently. Accordingly, to purify the exhaust gas in low engine load operation, it is required that an auxiliary catalytic apparatus is arranged at a position is not so far from the engine body.

It is suggested that the auxiliary catalytic apparatus is arranged on only one of the two exhaust passages and only the cylinder-group corresponding to the one exhaust passage on which the auxiliary catalytic apparatus is arranged is operated (part cylinder operation) in low engine load operation (for example, refer to Japanese Unexamined Patent Publications No. 7-133716 and No. 2001-227369).

In the above art, if the all cylinder operation is carried out at the engine start, the exhaust gas of the cylinder-group corresponding to the other exhaust passage on which the auxiliary catalytic apparatus is not arranged is emitted into the atmosphere without being purified because the catalyst of the main catalytic apparatus is not activated at the engine start. Further, it is also suggested that to make it possible to purify the exhaust gas by the main catalytic apparatus immediately after changing over from the part cylinder operation to the all cylinder operation, a combustion air-fuel ratio of the operating cylinders in the partly cylinders operation is made rich, and unburned fuel included in the exhaust gas of the rich air-fuel ratio is burned at the main catalytic apparatus with oxygen included in air exhausted from the non-operating cylinders and thus the temperature of the main catalytic apparatus is maintained at the catalytic activation temperature. However, this makes the fuel consumption of the operating cylinders in the partly cylinders operation deteriorate.

Therefore, an object of the present invention is to improve the deterioration of the exhaust emission at the engine start and the fuel consumption of the part cylinder operation in a device for purifying the exhaust gas of an internal combustion engine in which all cylinders of the multi-cylinder engine are divided into two cylinder-groups, each cylinder-group is provided with an exhaust passage from each exhaust manifold to an exhaust gas merging portion, and a main catalytic apparatus is arranged downstream of the exhaust gas merging portion.

SUMMARY OF THE INVENTION

A device for purifying the exhaust gas of an internal combustion engine according to claim 1 of the present invention is characterized by, in the engine, all cylinders of the multi-cylinders engine are divided into two cylinder-groups, each cylinder-group is provided with an exhaust passage from each exhaust manifold to an exhaust gas merging portion, and a main catalytic apparatus is arranged downstream of the exhaust gas merging portion, a first auxiliary catalytic apparatus is arranged in one of the two exhaust passages upstream of said exhaust gas merging portion, a second auxiliary catalytic apparatus is arranged in the other of said two exhaust passages, an amount of catalyst carried on said second auxiliary catalytic apparatus is smaller than that on said first auxiliary catalytic apparatus, and only the cylinder-group corresponding to said one of said two exhaust passages is operated at the engine starting.

A device for purifying the exhaust gas of an internal combustion engine according to claim 2 of the present invention is characterized by, in the engine, all cylinders of the multi-cylinders engine are divided into two cylinder-groups, each cylinder-group is provided with an exhaust passage from each exhaust manifold to an exhaust gas merging portion, and a main catalytic apparatus is arranged downstream of the exhaust gas merging portion, a first auxiliary catalytic apparatus is arranged in one of the two exhaust passages upstream of said exhaust gas merging portion, a second auxiliary catalytic apparatus is arranged in the other of said two exhaust passages, a heat capacity of said first auxiliary catalytic apparatus is lower than that of said second auxiliary catalytic apparatus, and only the cylinder-group corresponding to said one of said two exhaust passages is operated at the engine starting.

A device for purifying the exhaust gas of an internal combustion engine according to claim 3 of the present invention is characterized by, in the engine, all cylinders of the multi-cylinders engine are divided into two cylinder-groups, each cylinder-group is provided with an exhaust passage from each exhaust manifold to an exhaust gas merging portion, and a main catalytic apparatus is arranged downstream of the exhaust gas merging portion, a first auxiliary catalytic apparatus is arranged in one of the two exhaust passages upstream of said exhaust gas merging portion, a second auxiliary catalytic apparatus is arranged in the other of said two exhaust passages, a catalyst of said first auxiliary catalytic apparatus actives at a lower temperature than an activation temperature of a catalyst of said second auxiliary catalytic apparatus, and only the cylinder-group corresponding to said one of said two exhaust passages is operated at the engine start.

A device for purifying the exhaust gas of an internal combustion engine according to claim 4 of the present invention is characterized by, in the engine, all cylinders of the multi-cylinders engine are divided into two cylinder-groups, each cylinder-group is provided with an exhaust passage from each exhaust manifold to an exhaust gas merging portion, and a main catalytic apparatus is arranged downstream of the exhaust gas merging portion, a first auxiliary catalytic apparatus is arranged in one of the two exhaust passages upstream of said exhaust gas merging portion, a second auxiliary catalytic apparatus is arranged in the other of said two exhaust passages, an exhaust gas route length from the corresponding exhaust manifold to said first auxiliary catalytic apparatus is shorter than an exhaust gas route length from the corresponding exhaust manifold to said second auxiliary catalytic apparatus, and only the cylinder-group corresponding to said one of said two exhaust passages is operated at the engine starting.

A device for purifying the exhaust gas of an internal combustion engine according to claim 5 of the present invention is characterized by, in the device according to claim 4, said second auxiliary catalytic apparatus is arranged in said other of said two exhaust passages immediately upstream of said exhaust gas merging portion.

A device for purifying the exhaust gas of an internal combustion engine according to claim 6 of the present invention is characterized by, in the engine, all cylinders of the multi-cylinders engine are divided into two cylinder-groups, each cylinder-group is provided with an exhaust passage from each exhaust manifold to an exhaust gas merging portion, and a main catalytic apparatus is arranged downstream of the exhaust gas merging portion, a first auxiliary catalytic apparatus is arranged in one of the two exhaust passages upstream of said exhaust gas merging portion, a second auxiliary catalytic apparatus is arranged immediately downstream of said exhaust gas merging portion, and only the cylinder-group corresponding to said one of said two exhaust passages is operated at the engine starting.

In the device for purifying the exhaust gas of an internal combustion engine according to claim 1 of the present invention, the first auxiliary catalytic apparatus is arranged in one of the two exhaust passages upstream of the exhaust gas merging portion, the second auxiliary catalytic apparatus is arranged in the other of the two exhaust passages, an amount of catalyst carried on the second auxiliary catalytic apparatus is smaller than that on the first auxiliary catalytic apparatus, and only the cylinder-group corresponding to the one of the two exhaust passages is operated at the engine starting. Therefore, the exhaust gas in the partly cylinders operation at the engine starting is favorably purified by the first auxiliary catalytic apparatus because it carries a large amount of catalyst and is arranged in the exhaust passage near the engine body such that a catalyst carried thereon activates early. Accordingly, the exhaust emission at the engine start does not deteriorate.

Moreover, when the part cylinder operation is changed into the all cylinder operation, the cylinder-group corresponding to the other of the two exhaust passages starts to operate. Until the present time, heat of the engine has been transferring to the second auxiliary catalytic apparatus arranged in the other of the two exhaust passages near the engine body via the exhaust passage, and thus the temperature thereof becomes higher than that at the time of cranking. Therefore, immediately after the all cylinders operation starts, the catalyst of the second auxiliary catalytic apparatus activates to purify the exhaust gas. Thus, in the partly cylinders operation, it is not required to make the combustion air-fuel ratio rich and to maintain the main catalytic apparatus at a relative high temperature. Therefore, a deterioration of fuel consumption in the partly cylinders operation can be improved. Moreover, the second auxiliary catalytic apparatus arranged in the other of the two exhaust passages does not need to purify the exhaust gas at the engine starting including a relative large amount of unburned fuel. Therefore, an amount of catalyst carried on the second auxiliary catalytic apparatus can be made smaller than that on the first auxiliary catalytic apparatus. Therefore, in comparison with a case where the expensive auxiliary catalytic apparatus similar to the first auxiliary catalytic apparatus is arranged in the other exhaust passage, a cost of the exhaust system can be reduced.

In the device for purifying the exhaust gas of an internal combustion engine according to claim 2 of the present invention, the first auxiliary catalytic apparatus is arranged in one of the two exhaust passages upstream of the exhaust gas merging portion, the second auxiliary catalytic apparatus is arranged in the other of the two exhaust passages, a heat capacity of the first auxiliary catalytic apparatus is lower than that of the second auxiliary catalytic apparatus, and only the cylinder-group corresponding to the one of the two exhaust passages is operated at the engine start. Therefore, the exhaust gas in the partly cylinders operation at the engine starting is favorably purified by the first auxiliary catalytic apparatus because it is arranged in the exhaust passage near the engine body and has the small heat capacity such that a catalyst carried thereon activates early. Accordingly the exhaust emission at the engine starting does not deteriorate.

Moreover, when the partly cylinders operation is changed into the all cylinders operation, the cylinder-group corresponding to the other of the two exhaust passages starts to operate. Until the present time, heat of the engine has been transferring to the second auxiliary catalytic apparatus arranged in the other of the two exhaust passages near the engine body via the exhaust passage, and thus the temperature thereof becomes higher than that at the time of cranking. Therefore, immediately after the all cylinders operation starts, the catalyst of the second auxiliary catalytic apparatus activates to purify the exhaust gas. Thus, in the partly cylinders operation, it is not required to make the combustion air-fuel ratio rich and to maintain the main catalytic apparatus at a relative high temperature. Therefore, a deterioration of fuel consumption in the partly cylinders operation can be improved. Moreover, the second auxiliary catalytic apparatus arranged in the other of the two exhaust passages does not need to purify the exhaust gas at the engine starting. Therefore, the second auxiliary catalytic apparatus may not be made from an expensive material to reduce the heat capacity as the first auxiliary catalytic apparatus. Therefore, in comparison with a case where the expensive auxiliary catalytic apparatus similar to the first auxiliary catalytic apparatus is arranged in the other exhaust passage, a cost of the exhaust system can be reduced.

In the device for purifying the exhaust gas of an internal combustion engine according to claim 3 of the present invention, the first auxiliary catalytic apparatus is arranged in one of the two exhaust passages upstream of the exhaust gas merging portion, the second auxiliary catalytic apparatus is arranged in the other of the two exhaust passages, a catalyst of the first auxiliary catalytic apparatus actives at a lower temperature than an activation temperature of a catalyst of the second auxiliary catalytic apparatus, and only the cylinder-group corresponding to the one of the two exhaust passages is operated at the engine starting. Therefore, the exhaust gas in the partly cylinders operation at the engine starting is favorably purified by the first auxiliary catalytic apparatus because it is arranged in the in the exhaust passage near the engine body and has a catalyst with a low activation temperature such that the catalyst carried thereon activates more early. Accordingly the exhaust emission at the engine starting does not deteriorate.

Moreover, when the partly cylinders operation is changed into the all cylinders operation, the cylinder-group corresponding to the other of the two exhaust passages starts to operate. Until the present time, heat of the engine has been transferring to the second auxiliary catalytic apparatus arranged in the other of the two exhaust passages near the engine body via the exhaust passage, and thus the temperature thereof becomes higher than that at the starting time of cranking. Therefore, immediately after the all cylinders operation starts, the catalyst of the second auxiliary catalytic apparatus is activated to purify the exhaust gas. Thus, in the partly cylinders operation, it is not required to make the combustion air-fuel ratio rich and to maintain the main catalytic apparatus at a relative high temperature. Therefore, a deterioration of fuel consumption in the partly cylinders operation can be improved. Moreover, the second auxiliary catalytic apparatus arranged in the other of the two exhaust passages does not need to purify the exhaust gas at the engine starting. Therefore, the second auxiliary catalytic apparatus may not carry an expensive catalyst which activates at the low temperature as the first catalytic apparatus. Therefore, in comparison with a case where the expensive auxiliary catalytic apparatus similar to the first auxiliary catalytic apparatus is arranged in the other exhaust passage, a cost of the exhaust system can be reduced.

In the device for purifying the exhaust gas of an internal combustion engine according to claim 4 of the present invention, the first auxiliary catalytic apparatus is arranged in one of the two exhaust passages upstream of the exhaust gas merging portion, the second auxiliary catalytic apparatus is arranged in the other of the two exhaust passages, an exhaust gas route length from the corresponding exhaust manifold to the first auxiliary catalytic apparatus is shorter than an exhaust gas route length from the corresponding exhaust manifold to the second auxiliary catalytic apparatus, and only the cylinder-group corresponding to the one of the two exhaust passages is operated at the engine starting. Therefore, the exhaust gas in the partly cylinders operation at the engine starting is favorably purified by the first auxiliary catalytic apparatus because it is arranged in the exhaust passage near the engine body with the short exhaust gas route length from the exhaust manifold such that a catalyst carried thereon activates early. Accordingly the exhaust emission at the engine starting does not deteriorate.

Moreover, when the part cylinder operation is changed into the all cylinder operation, the cylinder-group corresponding to the other of the two exhaust passages starts to operate. Until the present time, heat of the engine has been transferring to the second auxiliary catalytic apparatus arranged in the other of the two exhaust passages near the engine body via the exhaust passage, and thus the temperature thereof becomes higher than that at the starting time of cranking. Therefore, immediately after the all cylinder operation starts, the catalyst of the second auxiliary catalytic apparatus activates to purify the exhaust gas. Thus, in the part cylinder operation, it is not required to make the combustion air-fuel ratio rich and to maintain the main catalytic apparatus at a relative high temperature. Therefore, a deterioration of fuel consumption in the partly cylinders operation can be improved.

Moreover, the second auxiliary catalytic apparatus arranged in the other of the two exhaust passages has the exhaust gas route length from the exhaust manifold longer than that of the first auxiliary catalytic apparatus arranged in the one of the two exhaust passages. When the temperature of the exhaust gas exhausted from the cylinders becomes very high at high engine load operation, the exhaust gas is kept at the very high temperature and flows into the first auxiliary catalytic apparatus in which the exhaust gas route length to the exhaust manifold is short, and thus there is a danger of melting the first auxiliary catalytic apparatus. Accordingly, it is required to make the combustion air-fuel ratio rich in the corresponding cylinders group and to lower the temperature of the exhaust gas exhausted from the cylinders. On the other hand, only the exhaust gas of which the temperature is lowered to some degree flows into the second auxiliary catalytic apparatus in which the exhaust gas route length to the exhaust manifold is long and thus a danger of melting it is small. Therefore, opportunities to make the combustion air-fuel ratio rich in the corresponding cylinder-group can be reduced. Thus, in comparison with a case where the second auxiliary catalytic apparatus is arranged in the other of the two exhaust passages at the short exhaust gas route length as the first auxiliary catalytic apparatus, the fuel consumption of the combustion with the rich air-fuel ratio to prevent from melting the second catalytic apparatus can be reduced.

The device for purifying the exhaust gas of an internal combustion engine according to claim 5 of the present invention is one in which the second auxiliary catalytic apparatus is arranged in the other of the two exhaust passages immediately upstream of the exhaust gas merging portion in the device according to claim 4. Therefore, the same effects as those of the device according to claim 4 can be obtained. Furthermore, in the partly cylinders operation, a part of the exhaust gas passing through the one of the two exhaust passages flows into the second auxiliary catalytic apparatus via the exhaust gas merging portion and thus the temperature of the second auxiliary catalytic apparatus can be elevated for the all cylinders operation.

In the device for purifying the exhaust gas of an internal combustion engine according to claim 6 of the present invention, the first auxiliary catalytic apparatus is arranged in one of the two exhaust passages upstream of the exhaust gas merging portion, the second auxiliary catalytic apparatus is arranged immediately downstream of the exhaust gas merging portion, and only the cylinder-group corresponding to the one of the two exhaust passages is operated at the engine starting. Therefore, the exhaust gas in the partly cylinders operation at the engine starting is favorably purified by the first auxiliary catalytic apparatus because it is arranged in the exhaust passage near the engine body such that a catalyst carried thereon activates early. Accordingly the exhaust emission at the engine starting does not deteriorate.

Moreover, when the partly cylinders operation is changed into the all cylinders operation, the cylinder-group corresponding to the other of the two exhaust passages starts to operate. In the part cylinders operation, the exhaust gas passing through the one of the two exhaust passages also flows into the second auxiliary catalytic apparatus immediately downstream of the exhaust gas merging portion and thus the temperature thereof becomes higher than that at the time of cranking. Therefore, immediately after the all cylinder operation starts, the catalyst of the second auxiliary catalytic apparatus is activated to purify the exhaust gas. Thus, in the part cylinder operation, it is not required to make the combustion air-fuel ratio rich and to maintain the main catalytic apparatus at a relative high temperature. Therefore, a deterioration of fuel consumption in the part cylinder operation can be improved.

Moreover, the second auxiliary catalytic apparatus is arranged immediately downstream of the exhaust gas merging portion and thus the exhaust gas route length of the second catalytic apparatus to the corresponding exhaust manifold is longer than that of the first catalytic apparatus arranged in the one of the two exhaust passages to the corresponding exhaust manifold. Accordingly, similarly with the device of claim 4 or 5, in comparison with a case where the second auxiliary catalytic apparatus is arranged in the other of the two exhaust passages at the short exhaust gas route length as the first auxiliary catalytic apparatus, a fuel consumption of the combustion with the rich air-fuel ratio to prevent from melting the second catalytic apparatus can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a device for purifying the exhaust gas of an internal combustion engine showing a first embodiment of the present invention.

FIG. 2 is a schematic view of a device for purifying the exhaust gas of an internal combustion engine showing a second embodiment of the present invention.

FIG. 3 is a schematic view of a device for purifying the exhaust gas of an internal combustion engine showing a third embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a schematic view, of a device for purifying the exhaust gas of an internal combustion engine, showing a first embodiment. In FIG. 1, reference numeral 1 a designates a first bank of V-type engine, and reference numeral 1 b designates a second bank thereof. Reference numeral 2 a designates a first intake manifold of the first bank 1 a, and reference numeral 2 b designates a second intake manifold of the second bank 1 b. A first intake passage 3 a is connected with the first intake manifold 2 a, and a second intake passage 3 b is connected with the second intake passage 2 b. Each throttle valve 4 a or 4 b is arranged in the first intake passage 3 a and the second intake passage 3 b to control amounts of intake air of the first bank 1 a and the second bank 1 b independently each other.

Reference numeral 5 a is a first exhaust manifold of the first bank 1 a, and reference numeral 5 b is a second exhaust manifold of the second bank 1 b. A first exhaust passage 6 a is connected with the first exhaust manifold 5 a, and a second exhaust passage 6 b is connected with the second exhaust passage 5 b. The first exhaust passage 6 a and the second exhaust passage 6 b are merged at an exhaust gas merging portion 7. A main catalytic apparatus 8 is arranged downstream of the exhaust gas merging portion 7.

The V type engine of the present embodiment carries out mainly an operation at the stoichiometric air-fuel ratio and a three-way catalytic apparatus is selected as the main catalytic apparatus 8. The main catalytic apparatus 8 is made relatively large. However, it is arranged under the floor of the vehicle and thus it can be easily mounted on the vehicle. Thus, a large amount of exhaust gas exhausted from all cylinders in high engine load operation can be sufficiently purified with the main catalytic apparatus 8. However, the temperature of the exhaust gas exhausted from each cylinder in low engine load operation is relatively low and the temperature of the exhaust gas becomes lower when it flows into the main catalytic apparatus 8. Therefore, the temperature of the main catalytic apparatus 8 cannot be maintained at the catalyst activation temperature and thus the purifying of the exhaust gas becomes insufficient.

Accordingly, in the present embodiment, a first auxiliary catalytic apparatus 9 a as a three-way catalytic apparatus is arranged in the first exhaust passage 4 a, and a second auxiliary catalytic apparatus 9 b as a three-way catalytic apparatus is arranged in the second exhaust passage 4 b. Therefore, when the low engine load operation is carried out in the fist bank 1 a and the second bank 1 b, the exhaust gas of the relative low temperature flows in the first auxiliary catalytic apparatus 9 a and the second auxiliary catalytic apparatus 9 b without a much lowering of the temperature and thus the temperature of catalyst carried on each auxiliary catalytic apparatus is maintained at the catalyst activation temperature to purify sufficiently the exhaust gas.

In the present embodiment, only the cylinders of the first bank 1 a are operated at the engine start, for example, from the starting time of cranking to a time at which an engine speed becomes the stable idle engine speed, or from the starting time of cranking to the finishing time of warming-up of the engine at which the idle operating with the increase of fuel is finished. On the other hand, the fuel injection into the cylinders of the second bank 1 b is stopped. Thus, the part cylinder operation is carried out. Therefore, the first auxiliary catalytic apparatus 9 a is arranged immediately downstream of the first exhaust manifold 5 a and the exhaust gas route length L1 from the first exhaust manifold 5 a to the first auxiliary catalytic apparatus 9 a is made considerably short, and thus the exhaust gas exhausted from each cylinder of the first bank 1 a flows into the first auxiliary catalytic apparatus 9 a with little lowering of the temperature and the temperature of the first auxiliary catalytic apparatus 9 a reaches the catalyst activation temperature early. Accordingly, at the engine start, the exhaust gas including a relative large amount of unburned fuel can be purified sufficiently by the first auxiliary catalytic apparatus 9 a.

When the part cylinder operation is changed into the all cylinder operation in which the cylinders of the second bank 1 b starts to operate after the engine start, heat of the engine has been transferring to the second auxiliary catalytic apparatus 9 b arranged in the second exhaust passage 6 b near the engine body via the second exhaust passage 6 b until the present time and thus the temperature thereof becomes higher than that at the starting time of cranking. Therefore, immediately after the exhaust gas from the second bank 1 b flows into the second auxiliary catalytic apparatus 9 b, the catalyst can activate to purify the exhaust gas. To make the temperature of the second auxiliary catalytic apparatus 9 b increase easily, in the present embodiment, the second auxiliary catalytic apparatus 9 b is arranged immediately downstream of the second exhaust manifold 5 b and the exhaust gas route length L2 from the second exhaust manifold 5 b to the second auxiliary catalytic apparatus 9 b is made considerably short similar to that of the first auxiliary catalytic apparatus 9 a.

However, the second auxiliary catalytic apparatus 9 b is not required to purify the exhaust gas including a relative large amount of unburned fuel at the engine starting, and thus in the present embodiment, an amount of catalyst carried on the second auxiliary catalytic apparatus 9 b is made smaller than that on the first auxiliary catalytic apparatus 9 a. Therefore, in comparison with a case where the expensive auxiliary catalytic apparatus similar to the first auxiliary catalytic apparatus 9 a is arranged in the second exhaust passage 6 b, the cost of the exhaust system can be reduced.

Furthermore, the second auxiliary catalytic apparatus 9 b is not needed to purify the exhaust gas in the engine starting and thus a heat capacity of the second auxiliary catalytic apparatus 9 b may be made larger than that of the first auxiliary catalytic apparatus by using cheap materials and the like. Therefore, in comparison with a case where the expensive auxiliary catalytic apparatus similar to the first auxiliary catalytic apparatus is arranged in the second exhaust passage 6 b, a cost of the exhaust system can be reduced.

Furthermore, the second auxiliary catalytic apparatus 9 b is not needed to purify the exhaust gas in the engine starting and thus the catalyst carried on the second auxiliary catalytic apparatus 9 b may be cheap and activate at a higher temperature than the activation temperature of the catalyst carried on the first auxiliary catalytic apparatus. Therefore, in comparison with a case where the expensive auxiliary catalytic apparatus similar to the first auxiliary catalytic apparatus is arranged in the second exhaust passage 6 b, a cost of the exhaust system can be reduced.

FIG. 2 is a schematic view of a device for purifying the exhaust gas of an internal combustion engine showing a second embodiment. Only the differences between the second embodiment and the first embodiment are explained as follows. In the second embodiment, the exhaust gas route length L1 from the first exhaust manifold 5 a to the first auxiliary catalytic apparatus 9 a is made shorter than the exhaust gas route length L2′ from the second exhaust manifold 5 b to the second auxiliary catalytic apparatus 9 b′, and the second auxiliary catalytic apparatus 9 b′ is desirable to be arranged on the second exhaust passage 6 b immediately upstream of the exhaust gas merging portion 7.

In such a construction, the exhaust gas in the part cylinder operation at the engine start is sufficiently purified by the first auxiliary catalytic apparatus 9 a. On the other hand, after the engine start, when the partly cylinders operation is changed into the all cylinders operation, heat of the engine has been transferring to the second auxiliary catalytic apparatus 9 b arranged in the second exhaust passage 6 b near the engine body via the second exhaust passage 6 b until the present time and thus the temperature thereof becomes higher than that at the start of cranking. Therefore, immediately after the exhaust gas from the second bank 1 b flows into the second auxiliary catalytic apparatus 9 b, the catalyst can activate to purify the exhaust gas. Moreover, when the second auxiliary catalytic apparatus 9 b′ is arranged immediately upstream of the exhaust gas merging portion 7, a part of the exhaust gas from the first bank 1 a in the part cylinder operation flows into the second auxiliary catalytic apparatus 9 b′ in the reverse direction via the exhaust gas merging portion 7. Therefore, the temperature of the second auxiliary catalytic apparatus 9 b′ can be elevated for the all cylinder operation.

By the way, when the temperature of the exhaust gas exhausted from the cylinders in high engine load operation and the like becomes very high, the exhaust gas is kept at the very high temperature and flows into the first auxiliary catalytic apparatus 9 a in which the exhaust gas route length L1 to the first exhaust manifold 5 a is very short, and thus there is a danger of melting the first auxiliary catalytic apparatus 9 a. Accordingly, it is required to make the combustion air-fuel ratio rich in each cylinder of the first bank 1 a and to lower the temperature of the exhaust gas exhausted from each cylinder of the first bank 1 a. In the present embodiment, the exhaust gas route length L2′ of the second auxiliary catalytic apparatus 9 b′ arranged on the second exhaust passage 6 b to the second exhaust manifold 5 b is longer than the exhaust gas route length L1 of the first auxiliary catalytic apparatus 9 a arranged on the first exhaust passage 6 a to the first exhaust manifold 5 a, and thus only the exhaust gas of which the temperature is lowered to some degree flows into the second auxiliary catalytic apparatus 9 b′ and a danger of melting it is small. Therefore, opportunities to make the combustion air-fuel ratio rich in each cylinder of the second bank 1 b can be reduced. Thus, in comparison with a case where the second auxiliary catalytic apparatus 9 b is arranged on the second exhaust passage 6 b at the short exhaust gas route length L1 as the first auxiliary catalytic apparatus 9 a, a fuel consumption of the combustion with the rich air-fuel ratio to prevent from melting the second catalytic apparatus can be reduced.

FIG. 3 is a schematic view of a device for purifying the exhaust gas of an internal combustion engine showing a third embodiment. Only differences between the third embodiment and the first embodiment are explained as follows. In the third embodiment, the second auxiliary catalytic apparatus 9 b″ is arranged immediately downstream of the exhaust gas merging portion 7 and the main catalytic apparatus 8 is arranged downstream of the second auxiliary catalytic apparatus 9 b″.

In such a construction, the exhaust gas in the partly cylinders operation at the engine starting is sufficiently purified by the first auxiliary catalytic apparatus 9 a. On the other hand, after the engine start, when the part cylinders operation is changed into the all cylinder operation, the exhaust gas in the partly cylinders operation has passed through the second auxiliary catalytic apparatus 9 b″ arranged immediately downstream of the exhaust gas merging portion 7 and the temperature of the second auxiliary catalytic apparatus 9 b″ has been elevated. Therefore, immediately after the exhaust gas from the second bank 1 b flows into the second auxiliary catalytic apparatus, the catalyst can be activated to purify the exhaust gas.

Moreover, as explained in the second embodiment, when the temperature of the exhaust gas in high engine load operation becomes very high, it is required to make the combustion air-fuel ratio rich in each cylinder of the first bank 1 a and to lower the temperature of the exhaust gas exhausted from each cylinder of the first bank 1 a to prevent from melting the first auxiliary catalytic apparatus 9 a. However, regarding the second auxiliary catalytic apparatus 9 b″ arranged immediately downstream of the exhaust gas merging portion 7, only the exhaust gas of which the temperature is lowered to some degree to pass through the second exhaust passage 6 b flows there, and thus even if the temperature of the exhaust gas in high engine load operation becomes very high, a danger of melting it is small. Therefore, opportunities to make the combustion air-fuel ratio rich in each cylinder of the second bank 1 b can be reduced. Thus, in comparison with a case where the second auxiliary catalytic apparatus 9 b″ is arranged on the second exhaust passage 6 b at the short exhaust gas route length L1 as the first auxiliary catalytic apparatus 9 a, a fuel consumption of the combustion with the rich air-fuel ratio to prevent from melting the second catalytic apparatus can be reduced.

In the above-mentioned second and third embodiments, the second auxiliary catalytic apparatus 9 b′ or 9 b″ may have an amount of carried catalyst similar to that of the first auxiliary catalytic apparatus 9 a, may have a heat capacity similar to that of the first auxiliary catalytic apparatus 9 a, and may carry a catalyst which activate at a low temperature similar to an activation temperature of a catalyst of the first auxiliary catalytic apparatus 9 a. However, the second auxiliary catalytic apparatus may have an amount of carried catalyst smaller than that of the first auxiliary catalytic apparatus 9 a, may have a heat capacity higher than that of the first auxiliary catalytic apparatus 9 a, and may carry a catalyst which is activated at a higher temperature than that the activation temperature of the first auxiliary catalytic apparatus 9 a.

In the above-mentioned embodiments, the main catalytic apparatus 8 is the three-way catalytic apparatus. However, in a case where the engine carries out a lean-burn operation, the main catalytic apparatus may be a NO_(x) catalytic apparatus. Furthermore, the engine carries out the part cylinder operation at the engine starting. However, of course, the engine may carry out the part cylinder operation in other than the engine starting, for example, in a low-engine-load operation. In the second bank 1 b, the part cylinder operation, in other than the engine start may be carried out.

In the above-mentioned embodiment, the engine is the V-type. However, this does not limit the present invention. The present invention can be also applied to an engine in which a plurality of cylinders are arranged in series and are divided into two groups, and each group is provided with an exhaust manifold. Moreover, when a plurality of cylinders are divided into three or more groups, the three or more exhaust passages upstream of the exhaust gas merging portion are divided into two groups and the present invention may be applied. 

1. A device for purifying the exhaust gas of an internal combustion engine in which all cylinders of the multi-cylinders engine are divided into two cylinder-groups, each cylinder-group is provided with an exhaust passage from each exhaust manifold to an exhaust gas merging portion, and a main catalytic apparatus is arranged downstream of the exhaust gas merging portion, characterized in that a first auxiliary catalytic apparatus is arranged in one of the two exhaust passages upstream of said exhaust gas merging portion, a second auxiliary catalytic apparatus is arranged in the other of said two exhaust passages, an amount of catalyst carried on said second auxiliary catalytic apparatus is smaller than that on said first auxiliary catalytic apparatus, and only the cylinder-group corresponding to said one of said two exhaust passages is operated at the engine start.
 2. A device for purifying the exhaust gas of an internal combustion engine in which all cylinders of the multi-cylinders engine are divided into two cylinder-groups, each cylinder-group is provided with an exhaust passage from each exhaust manifold to an exhaust gas merging portion, and a main catalytic apparatus is arranged downstream of the exhaust gas merging portion, characterized in that a first auxiliary catalytic apparatus is arranged in one of the two exhaust passages upstream of said exhaust gas merging portion, a second auxiliary catalytic apparatus is arranged in the other of said two exhaust passages, a heat capacity of said first auxiliary catalytic apparatus is lower than that of said second auxiliary catalytic apparatus, and only the cylinder-group corresponding to said one of said two exhaust passages is operated at the engine start.
 3. A device for purifying the exhaust gas of an internal combustion engine in which all cylinders of the multi-cylinders engine are divided into two cylinder-groups, each cylinder-group is provided with an exhaust passage from each exhaust manifold to an exhaust gas merging portion, and a main catalytic apparatus is arranged downstream of the exhaust gas merging portion, characterized in that a first auxiliary catalytic apparatus is arranged in one of the two exhaust passages upstream of said exhaust gas merging portion, a second auxiliary catalytic apparatus is arranged in the other of said two exhaust passages, a catalyst of said first auxiliary catalytic apparatus actives at a lower temperature than an activation temperature of a catalyst of said second auxiliary catalytic apparatus, and only the cylinder-group corresponding to said one of said two exhaust passages is operated at the engine start.
 4. A device for purifying the exhaust gas of an internal combustion engine in which all cylinders of the multi-cylinders engine are divided into two cylinder-groups, each cylinder-group is provided with an exhaust passage from each exhaust manifold to an exhaust gas merging portion, and a main catalytic apparatus is arranged downstream of the exhaust gas merging portion, characterized in that a first auxiliary catalytic apparatus is arranged in one of the two exhaust passages upstream of said exhaust gas merging portion, a second auxiliary catalytic apparatus is arranged in the other of said two exhaust passages, an exhaust gas route length from the corresponding exhaust manifold to said first auxiliary catalytic apparatus is shorter than an exhaust gas route length from the corresponding exhaust manifold to said second auxiliary catalytic apparatus, and only the cylinder-group corresponding to said one of said two exhaust passages is operated at the engine starting.
 5. A device for purifying the exhaust gas of an internal combustion engine according to claim 4, characterized in that said second auxiliary catalytic apparatus is arranged in said other of said two exhaust passages immediately upstream of said exhaust gas merging portion.
 6. A device for purifying the exhaust gas of an internal combustion engine in which all cylinders of the multi-cylinders engine are divided into two cylinder-groups, each cylinder-group is provided with an exhaust passage from each exhaust manifold to an exhaust gas merging portion, and a main catalytic apparatus is arranged downstream of the exhaust gas merging portion, characterized in that a first auxiliary catalytic apparatus is arranged in one of the two exhaust passages upstream of said exhaust gas merging portion, a second auxiliary catalytic apparatus is arranged immediately downstream of said exhaust gas merging portion, and only the cylinder-group corresponding to said one of said two exhaust passages is operated at the engine start. 